In this invention, the breaker layer is composed of at least one ply of parallel cords, which ply extends across the whole width of the tread width and the breaker cords are inclined with respect to the tire equator. A main purpose thereof is to increase the rigidity of the tread portion. The band layer is also composed of at least one ply of parallel cords laid substantially parallel to or at a relatively smaller angle to the tire equator. A main purpose of the band layer is to provide a hooping effect for the tread portion.
For examples, the following band layers have been known: one extending over the substantially whole width of a breaker layer or the tread width as shown in FIG. 12; one composed of a pair of axially spaced plies disposed at the axial edge portions of the breaker layer as shown in FIG. 13 to prevent separation of the breaker edge from the surrounding rubber; and one having edge portions folded to wrap the breaker edges therein to prevent separation of the breaker ply edges.
On the other hand, in order to improve various characteristics of the tire, e.g. road grip, drainage, running stability and the like, the tires are provided with grooves to form rib type tread patterns, block type tread patterns and the like, and tread elements, such as ribs or blocks are provided with sipes, if required.
In the conventional pneumatic tires, the above-mentioned band layers are disposed symmetrically with respect to the tire equator, regardless of the positions of the tread grooves and sipes, in order to reinforce the tread portion of the tire.
However, lateral grooves and sipes extending across a rib, decrease partially the rigidity of the tread, and as a result the tread element, the rib or divided rib moves easily, and uneven wear is apt to be caused. Therefore, it is preferable to adjust the rigidity of the tread portion according to the tread pattern and also the sizes and shapes of the tread elements.